TBX1 and chordoma: [4, 32] The secondary aggressive tumor was characterized by further accumulation of newly acquired point mutations, including pathogenic variants in genes involved in DNA repair and checkpoint mechanisms like TP53 and BRCA1. These variants probably contributed to the acquisition of an aggressive phenotype in the secondary tumor and further multiple cytogenetic changes, including the loss of chromosome region 6q, which encodes TBXT. This chromosomal deletion probably influenced the loss of brachyury expression, a hallmark of dedifferentiated chordoma.